Although ammonia is an essential compound in agriculture and industry, it is hazardous to humans and hence a large number of methods for decomposing ammonia in water and the air have been disclosed. For example, a method for removing ammonia through decomposition from water containing ammonia at a high concentration has been proposed: aqueous ammonia being sprayed is brought into contact with airflow to separate ammonia into the air and the ammonia is brought into contact with a hypobromous acid solution or sulfuric acid (Patent Literature 1). Another method has also been disclosed: ammonia is separated into the air by the same process as above and the ammonia is incinerated with a catalyst (Patent Literature 2). Another method has also been proposed: ammonia-containing wastewater is decomposed with a catalyst into nitrogen and water (Patent Literature 3). Disclosed catalysts for ammonia decomposition reactions are, for example, porous carbon particles containing a transition metal component, a manganese composition, an iron-manganese composition (Patent Literature 3); a chromium compound, a copper compound, a cobalt compound (Patent Literature 4); and platinum held in a three-dimensional network alumina structure (Patent Literature 5). Use of methods in which ammonia is decomposed by chemical reactions employing such catalysts can suppress generation of nitrogen oxides NOx. Methods have also been proposed in which manganese dioxide is used as a catalyst to thereby promote efficient thermal decomposition of ammonia at 100° C. or less (Patent Literatures 6 and 7).
In general, waste gas from semiconductor fabrication equipment contains ammonia, hydrogen, and the like. To completely remove the odor of ammonia, the amount of ammonia needs to be reduced to the ppm order. For this purpose, a method has been commonly used in which waste gas to be released from semiconductor fabrication equipment is passed through scrubbers so that water containing chemicals absorbs the hazardous gas. On the other hand, to achieve a low running cost without supply of energy, chemicals, or the like, a treatment for waste gas from semiconductor fabrication equipment has been proposed: ammonia is decomposed with a phosphoric acid fuel cell (Patent Literature 8).